IP Multimedia services provide a dynamic combination of voice, video, messaging, data, etc. within the same session. By growing the number of basic applications and the media which it is possible to combine, the number of services offered to the end users will grow, and the inter-personal communication experience will be enriched. This will lead to a new generation of personalised, rich multimedia communication services, including so-called “combinational IP Multimedia” services.
The UMTS (Universal Mobile Telecommunications System) is a third generation wireless system designed to provide higher data rates and enhanced services to subscribers. UMTS is a successor to the Global System for Mobile Communications (GSM), with an important evolutionary step between GSM and UMTS being the General Packet Radio Service (GPRS). GPRS introduces packet switching into the GSM core network and allows direct access to packet data networks (PDNs). This enables high-data rate packets switch transmissions well beyond the 64 kbps limit of ISDN through the GSM call network, which is a necessity for UMTS data transmission rates of up to 2 Mbps. UMTS is standardised by the 3rd Generation Partnership Project (3GPP) which is a conglomeration of regional standards bodies such as the European Telecommunication Standards Institute (ETSI), the Association of Radio Industry Businesses (ARIB) and others. See 3GPP TS 23.002 for more details.
The UMTS architecture includes a subsystem known as the IP Multimedia Subsystem (IMS) for supporting traditional telephony as well as new IP multimedia services (3GPP TS 22.228, TS 23.228, TS 24.229, TS 29.228, TS 29.229, TS 29.328 and TS 29.329 Releases 5 to 7). IMS provides key features to enrich the end-user person-to-person communication experience through the use of standardised IMS Service Enablers, which facilitate new rich person-to-person (client-to-client) communication services as well as person-to-content (client-to-server) services over IP-based networks. The IMS is able to connect to both PSTN/ISDN (Public Switched Telephone Network/Integrated Services Digital Network) as well as the Internet.
The IMS makes use of the Session Initiation Protocol (SIP) to set up and control calls or sessions between user terminals (or user terminals and application servers). The Session Description Protocol (SDP), carried by SIP signalling, is used to describe and negotiate the media components of the session. Whilst SIP was created as a user-to-user protocol, IMS allows operators and service providers to control user access to services and to charge users accordingly. The 3GPP has chosen SIP for signalling between a User Equipment (UE) and the IMS as well as between the components within the IMS.
Specific details of the operation of the UMTS communications network and of the various components within such a network can be found from the Technical Specifications for UMTS that are available from http://www.3gpp.org. Further details of the use of SIP within UMTS can be found from the 3GPP Technical Specification TS 24.228 V5.8.0 (2004-03).
FIG. 1 of the accompanying drawings illustrates schematically how the IMS fits into the mobile network architecture in the case of a GPRS/PS access network (IMS can of course operate over other access networks). Call/Session Control Functions (CSCFs) operate as SIP proxies within the IMS. The 3GPP architecture defines three types of CSCFs: the Proxy CSCF (P-CSCF) which is the first point of contact within the IMS for a SIP terminal; the Serving CSCF (S-CSCF) which provides services to the user that the user is subscribed to; and the Interrogating CSCF (I-CSCF) whose role is to identify the correct S-CSCF and to forward to that S-CSCF a request received from a SIP terminal via a P-CSCF.
A user registers with the IMS using the specified SIP REGISTER method. During the registration process, it is the responsibility of the I-CSCF to select a S-CSCF if a S-CSCF is not already selected. The I-CSCF receives the required S-CSCF capabilities from the home network's Home Subscriber Server (HSS), and selects an appropriate S-CSCF based on the received capabilities. It is noted that the allocation of an S-CSCF is key to controlling (and charging for) user access to IMS-based services.
When a registered user subsequently sends a session request to the IMS, the P-CSCF is able to forward the request to the selected S-CSCF based on information received from the S-CSCF during the registration process.
Within the IMS service network, Application Servers (ASs) are provided for implementing IMS service functionality. Application Servers provide services to end-users in an IMS system, and may be connected either as end-points over the 3GPP defined Mr interface, or “linked in” by an S-CSCF over the 3GPP defined ISC interface.
3GPP TS 32.240 and 3GPP TS 32.260 define the IMS charging architecture and principles and thereby defines when to send charging information and when not to send charging information.
In the context of any service execution, at least one charging determination (or triggering) point must exist, either for generating accounting records (for offline charging) or for requesting quota/authorization (for online charging) for this particular service or session. Offline charging is a post-paid type of charging scheme whereby charging is performed after a service has been consumed by the user; for example the user might receive a monthly bill showing chargeable items from the previous month. Online charging is a pre-paid type of charging scheme, where network entities would consult with the charging system before allowing a user access to the requested service (strictly speaking, online charging can be used for post-paid as well; normally it is pre-paid but it can also be used to serve as spending control, setting usage limits at service introductions and so on).
According to 3GPP TS 32.260 and 3GPP TS 32.299, different IMS nodes can act as Charging Triggering Functions (CTFs); in particular, either the S-CSCF or the ASs (or both) can act as CTF for most traffic events and all service invocations. The Charging Triggering Functions are adapted to generate charging information for a service/event and to send that information to a Charging Control System. This information can then be used, for example, when billing the user or at inter-operator settlements.
The present applicant has appreciated the following problem with the situation as it is currently specified.
Since, as mentioned above, a number of different IMS nodes can act as Charging Triggering Functions (CTFs), and since each such node has its own unique function, the data available for a CTF will generally differ from CTF to CTF, and thus also the charging information generated. A certain charging model used by an operator may require charging data from more than one CTF to be able to perform correct rating of the service/event.
Consolidation of data from different CTFs costs time and resources and is normally avoided if at all possible in the case of offline charging (Rf interface). Consolidation of data in real-time is not generally feasible, which generally rules out consolidation of online data (Ro interface).
Assuming that the same or similar rating decisions are taken for user charging, irrespective of whether offline or online charging is used, the charging models should be constructed so that consolidation is avoided as far as possible; however this is not always possible, or it will hamper differentiation of services and tariffs.
It is desirable to address the above issue as identified and explained by the present applicant.